1. Field of the Invention
The present invention particularly provides, in a photovoltaic device comprising a first electrode composed of zinc oxide, a photovoltaic device whose characteristics are improved, and a method of fabricating the same.
2. Description of Prior Art
Photovoltaic devices composed of an amorphous semiconductor such as amorphous silicon, amorphous silicon carbide, or amorphous silicon germanium are low in fabrication cost and can be easily increased in area. Accordingly, the photovoltaic devices have been developed as low-cost solar cells.
Referring to a cross-sectional view of FIG. 18, description is made of a photovoltaic element composed of an amorphous semiconductor. A photovoltaic element 10 composed of an amorphous semiconductor comprises a first electrode 2, a photovoltaic conversion layer 3 composed of a lamination body of p-type, i-type, and n-type amorphous semiconductor layers 3p, 3i, and 3n, and a second electrode 4 laminated in this order on a substrate 1. When a translucent member such as glass or plastic is used as the substrate 1, the first electrode 2 is composed of a translucent conductive material, and the second electrode 4 is composed of a highly reflective conductive material.
As the translucent conductive material composing the first electrode 2, tin oxide (SnO2) has been conventionally used. However, it has been examined whether or not zinc oxide (ZnO) is used in order to achieve low cost in recent years, so that a photovoltaic element having high photovoltaic conversion characteristics has been obtained.
For example, a first electrode 2 composed of ZnO is formed by sputtering on a substrate 1 composed of glass, a photovoltaic conversion layer 3 composed of a lamination body of a p-type layer 3p having a thickness of approximately 150 xc3x85 composed of p-type amorphous silicon carbide, an i-type layer 3i having a thickness of approximately 4000 xc3x85 composed of i-type amorphous silicon, and an n-type layer 3n having a thickness of approximately 200 xc3x85 composed of n-type amorphous silicon is then formed by plasma CVD (Chemical Vapor Deposition), and a second electrode 4 composed of Ag is laminated using sputtering, thereby fabricating a photovoltaic element 10.
As a result of changing the thickness of the first electrode 2 to various thicknesses to measure photovoltaic conversion efficiency, high photovoltaic conversion efficiency in excess of 10.5% is obtained in a case where the thickness of the first electrode 2 composed of ZnO is in the range of approximately 2100 xc3x85 to approximately 5000 xc3x85, as shown in a characteristic view of FIG. 19.
In a photovoltaic element using ZnO for a first electrode, however, high photovoltaic conversion efficiency is obtained, as described above. In the case of an integrated photovoltaic device, sufficient characteristics are not obtained.
The present invention has been made in order to solve such a conventional problem, and its object is to provide a photovoltaic device capable of obtaining superior photovoltaic conversion characteristics when ZnO is used for a first electrode and a method of fabricating the same.
A photovoltaic device according to the present invention is characterized by comprising a substrate; a plurality of first electrodes separated from one another by separating trenches on the substrate; a photovoltaic conversion layer provided on the substrate, including the first electrodes; and a plurality of second electrodes provided on the photovoltaic conversion layer and separated from one another by second separating trenches, and in that the thickness of a side end in the first electrode in the vicinity of the separating trench existing between the first electrode and the adjacent first electrode is larger than the thickness of an element region in the first electrode.
According to such construction, a portion irradiated with laser beams for forming the separating trench is formed to a thickness larger than the thickness of the element region. As a result, the first electrodes can be formed in a separated manner with a high yield, thereby making it possible to provide a photovoltaic device having high photovoltaic conversion characteristics.
The photovoltaic device is characterized in that the first electrode is composed of zinc oxide, is characterized in that the thickness of the side end in the first electrode is not less than 5000 xc3x85, and is characterized in that the thickness of the element region in the first electrode is in the range of approximately 2100 xc3x85 to approximately 5000 xc3x85.
Furthermore, the photovoltaic device is characterized in that a textured surface is formed in the element region in the first electrode, and is characterized in that the element region in the first electrode is made thinner than the side end in the step of forming the textured surface.
Alternatively, the photovoltaic device is characterized in that the thickness of the side end in the first electrode is larger than the thickness of the element region by forming a laser beam absorbing member.
As described in the foregoing, the thickness of the side end in the vicinity of the separating trench in the first electrode is made larger than the thickness of the element region by providing the laser beam absorbing member on the first electrode. As a result, the first electrodes can be formed in a separated manner with a high yield, thereby making it possible to provide a photovoltaic device having high photovoltaic conversion characteristics.
In addition thereto, the photovoltaic device is characterized in that the first electrode is divided into a plurality of parts by laser beam irradiation.
The present invention is directed to a photovoltaic device, characterized by comprising a substrate; an insulation thin film provided in a portion corresponding to an element region on the substrate; a plurality of first electrodes formed on the substrate, including the insulation thin film, and separated from one another by separating trenches; a photovoltaic conversion layer provided on the substrate, including the first electrodes; and a plurality of second electrodes provided on the photovoltaic conversion layer and separated from one another by second separating trenches, and in that the thickness of a side end in the first electrode in the vicinity of the separating trench existing between the first electrode and the adjacent first electrode is larger than the thickness of the element region in the first electrode.
According to such construction, the portion irradiated with the laser beams for forming the separating trench is formed to a thickness larger than the thickness of the element region. Further, it has a good film orientation. As a result, the first electrodes can be formed in a separated manner with a high yield, thereby making it possible to provide a photovoltaic device having high photovoltaic conversion characteristics.
The photovoltaic device is characterized in that the first electrode is composed of zinc oxide, and is characterized in that the insulation thin film is selected from silicon dioxide (SiO2), aluminum oxide (Al2O3), and titanium oxide (TiO2).
The photovoltaic device is characterized in that the element region in the first electrode is made thinner than the side end in the step of forming the textured surface.
A method of fabricating a photovoltaic device according to the present invention is a method of fabricating a photovoltaic device comprising on a substrate a plurality of photovoltaic elements each composed of a lamination body of a first electrode, a photovoltaic conversion layer, and a second electrode, characterized by comprising the steps of forming an electrode film on the substrate; thinning a region serving as an element region in the electrode film; irradiating laser beams into a separating region in the electrode film, and removing the electrode film in a portion irradiated with the laser beams, to form a plurality of first electrodes in a separated manner.
According to the above-mentioned construction, the portion irradiated with the laser beams for forming the separating trench is formed to a thickness larger than that of the element region. As a result, the first electrodes can be formed in a separated manner with a high yield, thereby making it possible to provide a photovoltaic device having high photovoltaic conversion characteristics.
The method is characterized in that the electrode film is composed of zinc oxide, is characterized in that the electrode film is formed to a thickness of not less than 5000 xc3x85, and is characterized in that in the step of thinning the region serving as the element region in the electrode film, the thickness of the region serving as the element region is in the range of approximately 2100 xc3x85 to approximately 5000 xc3x85.
Furthermore, the method is characterized in that in the step of thinning the region serving as the element region in the electrode film, a textured surface is formed on a surface of the region serving as the element region, and is characterized in that the step of thinning the region serving as the element region in the electrode film is carried out after the step of forming the plurality of first electrodes in a separated manner.
Alternatively, the present invention is directed to a method of fabricating a photovoltaic device comprising on a substrate a plurality of photovoltaic elements each composed of a lamination body of a first electrode, a photovoltaic conversion layer, and a second electrode, characterized by comprising the steps of forming an electrode film on the substrate; providing a laser beam absorbing member on a separating region in the electrode film; and irradiating laser beams into the laser beam absorbing member, removing the laser beam absorbing member in a portion irradiated with the laser beams, together with the electrode film just below the laser beam absorbing member, to form a plurality of first electrodes in a separated manner. According to the above-mentioned construction, the thickness of the side end in the vicinity of the separating trench in the first electrode can be made larger than the thickness of the element region by providing the laser beam absorbing member on the first electrode. As a result, the first electrodes can be formed in a separated manner with a high yield, thereby making it possible to provide a photovoltaic device having high photovoltaic conversion characteristics.
Furthermore, the method is characterized in that the electrode film is formed of zinc oxide, and is formed to a thickness of approximately 2100 xc3x85 to approximately 5000 xc3x85.
A method of fabricating a photovoltaic device according to the present invention is a method of fabricating a photovoltaic device comprising on a substrate a plurality of photovoltaic elements each composed of a lamination body of a first electrode, a photovoltaic conversion layer, and a second electrode, characterized by comprising the steps of forming an insulation thin film in a region corresponding to an element region on the substrate; forming an electrode film on the substrate, including the insulation thin film; etching the electrode film, to make the electrode film serving as an element region positioned on the insulation thin film thinner than the electrode film positioned in the other region; and irradiating laser beams into a separating region in the electrode film, and removing the electrode film in a portion irradiated with the laser beams, to form a plurality of first electrodes in a separated manner.
As described in the foregoing, when the insulation thin film is selectively provided on the substrate, the crystallizability of the first electrode which is directly formed on the substrate is higher than that of the first electrode which is formed on the insulation thin film. When etching using a solution of hydrochloric acid (HC1) or a solution of acetic acid (CH3COOH) is performed, therefore, the first electrode in the element region is etched faster than the first electrode at the side end. As a result, the thickness of the side end is made larger than the thickness of the element region. The portion irradiated with the laser beams for forming the separating trench is formed to a thickness larger than that of the element region. Further, it has a good film orientation. As a result, the first electrodes can be formed in a separated manner with a high yield, thereby making it possible to provide a photovoltaic device having high photovoltaic conversion characteristics.
The method is characterized in that the electrode film is formed of zinc oxide, and is characterized in that the insulation thin film is selected from silicon dioxide (SiO2), aluminum oxide (Al2O3), and titanium oxide (TiO2).
The method is characterized in that in the step of thinning the region serving as the element region in the electrode film, the thickness of the region serving as the element region is in the range of approximately 3500 xc3x85 to approximately 5500 xc3x85, and a textured surface is formed on a surface of the electrode film.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.